1. Field of the Invention
The present invention generally relates to devices employing charged particle beams and, more particularly, to arrangements for precision deflection of electron beams.
2. Description of the Prior Art
It is well-known that a beam of charged particles can be deflected by imposing an electrostatic field across the beam path. Such electrostatic deflection has been employed, for example, in cathode ray tubes using orthogonally oriented pairs of plates which can be oppositely charged to deflect an electron beam substantially as desired.
However, such plates must be placed within the evacuated chamber in close proximity to the beam and are thus subject to several deleterious effects including heating, dimensional changes and damage from impingement of the beam as well as having materials deposited thereon or reacting therewith. The angle of beam deflection is also limited and significant distortions are produced as the limit of deflection is approached. Capacitance of the plates also limits the speed with which a change in deflection can be achieved. Solid metal plates can be used only in areas of the electron beam column where there are no dynamic magnetic fields present (i.e. deflection yokes, alignment coils, dynamic focus coils and stigmatism correctors and the like) that create eddy currents which affect deflection speed and positional accuracy. For all practical lithography tools, the superposition of one or more of these fields is required.
Nevertheless, as precision and resolution of cathode ray tubes, electron beam lithography tools, electron microscopes and the like have increased and necessary departures from ideal geometry of magnetic deflection systems have become more significant, electrostatic deflection arrangements for fine high speed adjustment of electron beam trajectory has been introduced. Fine adjustments which are found to be desirable may also be best achieved by use of more than two pairs of electrostatic poles placed other than orthogonally to each other. Such arrays of electrostatic poles are generally referred to as multipole deflectors.
An example of a multipole deflector is disclosed in IBM Technical Disclosure Bulletin Vol. 30, No. 6, pp. 27-28 (November 1987) which is hereby fully incorporated by reference. This publication acknowledges that extremely high dimensional accuracy is required which is difficult to achieve. This problem and the problem of development of eddy currents is approached by forming the multipole deflector from a tube of insulating material having a low coefficient of thermal expansion such as quartz or ceramic, cutting axial slots in the tube less than the full length thereof to leave a continuous wall around each end of the tube for holding the poles in position. The slotted tube is then plated with a non-reactive (to avoid oxide formation and subsequent charging problems) conductor material such as gold, removing the plating at the ends of the tube to electrically separate the poles and installing grounding caps at the ends of the tube where plating was removed to prevent charging.
While this structure provided results superior to other arrangements using individually stacked poles, the process of making this multipole deflector was difficult and unreliable due to coating defects which affected the beam although not readily apparent from inspection and/or testing. Further, eddy.currents in the thin plating layer, while significantly reduced, were not fully suppressed and some charging effects not fully remedied by the grounding caps were encountered.
In summary, no multipole deflector structure is known which is mechanically robust and dimensionally stable that can be repeatably and reliably manufactured with extremely high dimensional accuracy by a practical method and which is free from both eddy current effects and charging effects which have required use of materials having radically differing conduction properties. That is, eddy current suppression has required use of insulating materials which are subject to charging and suppression of charging effects and provision of well-regulated electrostatic fields requires conductors which are subject to eddy currents. While eddy currents may be suppressed to a significant degree by formation of extremely thin conductors such as plated gold, such thin coatings are subject to irregularities and non-uniformities which can affect the beam and the function of the conductor to deflect the beam.
Thus, no known multipole deflector arrangement has been found fully satisfactory to allow the development of the positional accuracy of which current charged particle beam systems are otherwise capable. Moreover, the known multipole deflector arrangement providing the currently highest level of performance requires a complex and difficult manufacturing process in which development of regions potentially subject to charging effects cannot be avoided and in which there is a trade-off regarding conductor thickness for suppressing eddy current effects and developing conductor films of adequate uniformity.
It is therefore an object of the present invention to provide a multipole deflector arrangement which is mechanically robust and can be easily and economically manufactured with high dimensional accuracy and stability and which is not subject to charging or eddy current effects.
It is another object of the invention to overcome problems of reliable manufacture and susceptibility to charging and eddy current effects of multipole deflectors made from insulating tubes with thin conductive coating(s).
In order to accomplish these and other objects of the invention, a multipole deflector element and charged particle beam tool including the same are provided wherein the multipole element comprises a plurality of poles in the form of sectors of a tube formed from a conductive material having a bulk material resistivity of 1000 microohm-cm or greater, said poles being supported by an insulating collar.
In accordance with another aspect of the invention, a method of forming a multipole deflector element for a particle beam tool is provided including the steps of cutting slots between but not reaching ends of a tube of conductive/resistive material parallel to an axis of the tube to form sectors connected by end rings, bonding a ring of insulating material to the sectors between said end rings, and removing the end rings.